1. Field of Invention
The present invention relates to a parking brake system, and more particularly to a driving device for a parking brake system that is durable and efficient.
2. Description of the Related Art
A conventional mechanical parking brake system (i.e. hand brake) comprises a lever in a car. When a driver pulls the lever for parking a car, brake mechanisms of the car are actuated to prevent the car from moving. However, due to the lever of the conventional mechanical parking brake system occupies a space in the car it does not conform to an electronic trend of a modern automobile industry.
A conventional electronic parking brake system uses electronic controllers to control the driving device of the parking brake system, so users can use a button or the like to replace a lever for controlling the parking brake system. Conventional driving devices of an electronic parking brake system can be classed with a single cable type and a dual cable type according to the numbers of the brake cables. Like the US Publication No. US20060231352 disclosed a “Electronic Drive of a Parking Brake” and U.S. Pat. No. 6,533,082 patent disclosed a “Electric Parking Brake”. Both are classed with the dual cable type. Nevertheless, the dual cable type driving device primarily has disadvantages as follows:
1. It has multiple connecting interfaces that increase manufacturing costs and assembling difficulty.
2. It must have a balancer inside.
A conventional driving device of the single cable type like US Publication No. US2007131494 disclosed a “Parking brake comprising a cable traction device”. The patent mainly comprises two deflection rollers. The deflection rollers are arranged in such a manner that a connection line between rotational axis of the deflection rollers can be rotated with respect to a main driving axis line. Therefore, a brake cable can be tightened with an essentially equal force in opposite directions.
However, the conventional driving device of the single cable type has some problems needed to overcome, comprising that the brake cable is tightened regularly when the brake cable is substantially bent with two reversal deflections. Therefore, the brake cable is damaged easily and a life span of the brake cable is shortened. Additionally, because the brake cable is substantially bent, a mechanical efficiency is lowered.
To overcome the shortcomings, the present invention provides a driving device for a parking brake system to mitigate or obviate the aforementioned problems.